Y Windows
The Y Windows, also known as Y Window System, is a windowing system, consisting of a window server and a client library for writing applications, written by Mark Thomas. It is intended to be a successor to the X Window System. It differs from the X Window System in having an integrated widget set and ground-up support for things like an alpha channel, which allows transparent or translucent windows.

Yacc: Yet Another Compiler Compiler
Yacc, abbreviated from "Yet Another Compiler Compiler", is a Unix system tool program for generating C or C++ code for a parser. Yacc is a command-line tool that accepts a grammar description (in a text file) as input and generates the code for a parser for that grammar as output. Parsers are useful in many systems other than just compilers, such as for reading the contents of a configuration file stored in a system's flash memory. Yacc was developed by Stephen C. Johnson at AT&T for the Unix operating system. Later compatible programs were written, such as Berkeley Yacc, GNU bison, MKS yacc and Abraxas yacc. Each offers slight improvements and additional features over the original Yacc, but the concept has remained the same. Yacc has also been rewritten for other languages, including Ratfor, EFL, ML, Ada, Java, and Limbo.

YafRay: Yet Another Free Raytracer
YafRay, abbreviated from "Yet Another Free Raytracer", is an open source ray tracing program that uses an XML scene description language. It has recently been integrated into, and is often used to render scenes made in, the 3D modelling software Blender.

Z88DK
Z88DK is a Small-C-derived cross compiler for a long list of Z80 based computers. The name derives for that it was originally developed to target the Cambridge Z88. Z88DK is much developed from Small-C and accepts many features of ANSI C with the notable exception of multi-dimensional arrays and function pointers.

ZIP File Format
The ZIP file format is a popular data compression and archival format. A ZIP file contains one or more files that have been compressed or stored. The ZIP format was originally designed by Phil Katz for PKZIP. However, many software utilities other than PKZIP itself are now available to create, modify or open ZIP files, notably WinZip, BOMArchiveHelper, PicoZip, Info-ZIP, WinRAR, IZArc and 7-Zip. ZIP files generally use the file extensions ".zip" or ".ZIP" and the MIME media type application/zip.

ZipGenius
ZipGenius' is a freeware file archiver designed for Microsoft Windows users, developed by M.Dev Software. It uses eg. 7-Zip format, and can also handle a number of other archive formats. It is a freeware product and is presented in two editions: STANDARD and SUITE. While the suite edition includes optional modules of the ZipGenius project (oriented to experts and power-users), the standard setup package simply includes the main ZipGenius application.

Zipping
Zipping refers to the process of compressing a file so it takes up less space. The compress files after zipping is called a zip file. There are two types of Zip files, normal (requiring a program to extract them) and self-executing that open up automatically. PKZip and WinZip are popular zipping and unzipping programs.

Zlib
zlib is an open-source, cross-platform data compression library. It was created by Jean-loup Gailly and Mark Adler as a general-purpose abstraction of the DEFLATE compression algorithm used in their gzip file compression program.